The present invention relates to a device for insufflating gas, such as CO2, into a corporeal cavity of a human or animal body and including a source of gas and a control unit regulating the gas pressure and gas flow through a needle during an endoscopic surgery.
A good number of embodiments of generic type devices for insufflating gas are known. With regard to this, reference is made to DE-A-30 00 218, EP-B-O 169 972, DE-C-36 11 018, U.S. Pat. No. 4,874,362 and DE-A-42 19 859. Moreover, reference is explicitly made to these printed publications for the explanation of all details not made more apparent herein.
A typical device for insufflating gas 10 into a corporeal cavity 30, as shown in FIG. 3, possesses a connection for a gas source 32, such as a pressure cylinder, and the capability of setting the gas pressure and the gas flow. For this purpose, the known devices are provided with, for example, a pressure and the gas flow sensors. Also, the known devices are provided with, a pressure/gas flow regulator 34 which reduces the pressure of the gas source to a insufflation pressure (desired gas pressure), which can be set, of typically between 0 and 50 mm Hg, and a flow regulator which sets the gas flow to a value (desired gas flow).
In the generic devices described in the aforementioned printed publications, the gas pressure or the gas flow can not only be controlled, but they are also regulated. For this purpose, these devices are provided with a measuring device having sensors for the actual gas pressure 36 and the actual gas flow 38, and with a control unit 40 to which the output signals from these sensors are applied and which controls the pressure regulator and the flow regulator 34, as shown in FIG. 3.
However, a problem with the known devices for insufflating gas into a corporeal cavity is measuring the gas pressure, because it is usually impossible or only with great effort to measure the gas pressure directly inside the corporeal cavity. Due to the streaming gas and the drop in pressure (i.e. generated thereby), measuring the pressure outside the corporeal cavity leads to a measuring error, which cannot be readily tolerated in medical applications.
Therefore, it is proposed in that order to measure the xe2x80x9cstaticxe2x80x9d gas pressure P, to reduce the gas flow Q to the value 0 and to measure the gas pressure when the gas flow actually reaches the value 0 xe2x80x9cstaticallyxe2x80x9d. With regard to this, reference is made to FIG. 6 of U.S. Pat. No. 4,874,362 and the respective specification. Although this method has the advantage that it permits relatively accurate measurement of the gas pressure, it has the disadvantage that it does not permit an even relatively constant gas supply.
Furthermore, it has been proposed to calculate the pressure actually prevailing in the corporeal cavity from the output signal of the sensor while taking into account the flow resistance of the tube instrument and the insufflation instrument, such as a Verres needle, between the pressure sensor and the corporeal cavity whose pressure is to be determined.
However, in practice determining the flow resistance and the drop in pressure between the pressure sensor and the corporeal cavity has proven difficult.
The invented device is distinguished by the fact that, the control unit calculates the drop in pressure Pdrop between the location of the pressure sensor and the corporeal cavity and therefore the actual gas pressure Pabd inside the corporeal cavity (intraabdominal pressure), as a function of the gas pressure Pfill measured outside the corporeal cavity and the measured gas flow Q. The calculated drop in pressure Pdrop as the function of Q is less or at the most equals the actual drop in pressure. The control unit calculates the gas pressure Pabd in an event and/or time controlled manner during normal insufflation and regulates the insufflation on the basis of the calculated gas pressure Pabd.
An object of the present invention is to further develop a device for insufflating gas into a corporeal cavity of a human or animal body in such a manner that the drop in pressure between the pressure sensor and the corporeal cavity and therefore the pressure inside the corporeal cavity can be determined as accurately as possible while ensuring highest possible patient safety.
The present invention is based on a generic device for insufflating gas into a corporeal cavity of a human or animal body and further improves this device according to the present invention as follows:
For calculating the drop in pressure Pdrop between the site of the pressure sensor and the corporeal cavity, whose pressure as the actual gas pressure Pabd (intraabdominal pressure) is the relevant pressure, the control unit uses one of a plurality of simple functions of the gas pressure Pfill measured outside the corporeal cavity and of the measured gas flow Q. On the basis of these functions, the calculated pressure drop Pdrop as the function of Q is less than or at most equals the actual pressure drop. Furthermore, the control unit continuously calculates the event and/or time controlled gas pressure Pabd during the normal insufflation and regulates insufflation on the basis of the calculated gas pressure Pabd Thus, unlike prior art systems, no single complicated mathematical function is used to express the variation in pressure drop from the gas flow rate throughout the entire range of values of gas flow rate. Instead, the function to be employed is selected from a plurality of functions based upon the flow rate. Thus, in the example more fully discussed below, a function having a simple square dependency on the pressure drop of the gas flow rate is used only at low gas flow rates, while a function having a simple linear dependency is used only at high gas flow rates. Thus, to cover the entire range of gas flow rates, either one function or the other is used, as expedient.
Based on the invention method, the intraabdominal pressure prevailing inside the corporeal cavity is not underestimated at any time. As the intraabdominal pressure prevailing inside the corporeal cavity is continuously determined, contrary to the known devices in which the intraabdominal pressure is determined at relatively large time intervals, a too high a pressure can never occur inside the corporeal cavity.
Tests have shown that at usual gas flows of up to 20 liter/min, as are used in medical insufflation procedures, it is sufficient to employ two functions for determining the drop in pressure, which are drawn upon for certain flow rates.
Thus, according to one aspect of the Invention, it is preferred that when the flow rates are less than a specific flow rate Qums, a square dependency of the pressure drop on the flow rate is utilized. At flow rates that are greater than this specific flow rate, it is preferred if a linear dependency of the drop in pressure on the flow rate is utilized. Using these two functions ensures that the calculated drop in pressure is always less than or at most equals the actually occurring drop in pressure between the measurement site and inside the body, so that a too high a pressure can never occur inside the body cavity.
The invented principle for determining the pressure drop in the tubes and in the other instruments in dependency on the flow rate can be applied in a great variety of devices.
For instance, it can be applied in devices in which the control unit determines the constants K1 and K2 while taking into account the flow resistance of the insufflation instruments. In particular, it is conceivable that these constants are calculated on the basis of expectancy values and the respective length of the tube instrument as well as of the employed instrument.
However, it is particularly advantageous that according to another aspect of the invention, in order to determine the constants K1, and K2, the control unit determines the values Pfill and Q (to be utilized in the equation in the resolution of these equations for the constants K1, and K2) at essentially constant gas flow Q and the value Pabd in a gas flow xe2x80x9cdistinctly reducedxe2x80x9d compared to normal gas flow. The flow can be lowered to xe2x80x9czeroxe2x80x9d or to a value differing distinctly from zero, as described in the not prepublished PCT/DE95/00756.
This application describes that while the pressure is being measured, the actual gas flow is set at a value between 10 and 40% of the desired gas flow.
In both instances, the gas flow prior to reduction, that is the gas flow during xe2x80x9cnormalxe2x80x9d insufflation, is taken for correcting the pressure value of the gas flow measured by the pressure sensor.
As the flow resistance of the insufflation instrument may change, by way of illustration due to an unintended bend in the tubing, according to still another aspect of the invention, it is preferred that the control unit uses the constants K1, and K2 for calculating the intraabdominal pressure in the corporeal cavity only for the next cycle, i.e. until the next drop in flow. Therefore, in the preferred embodiment, the control unit calculates the constants K1, and K2 anew for each cycle from values determined in the preceding cycle.
The invention also discloses a method of determining the value of the flow or the flow rate Qums at which the control unit switches between linear and square dependency of the drop in pressure in the flow rate. The value of the flow rate at which it is switched is determined by the point of intersection of the linear and the square dependency of the drop in pressure Pdrop at the flow rate Q for each determined constant K1 and K2.
The measurement principle of the invented device can be applied in a great variety of devices for insufflation of gas in corporeal cavities. It is particularly advantageous to use the measuring principle in devices which can also generate high flow rates ( greater than 10 l/min.), because in devices of this type, the influence of the flow rate is especially great due to the large variation of the flow rate.
If, for instance, a maximum flow rate of 30 l/min. and an interval common in the state of the art of approximately 2 seconds between successive measurements of the pressure inside a corporeal cavity at a gas flow rate reduced to 0 is assumed, in the case of an especially small corporeal cavity (small patients, children), which in this case is usually less than 3 liters, there is a considerable rise in pressure, because a gas volume of one liter is transported into the corporeal cavity within 2 seconds.
The invented device extrapolates the pressure inside the body continuously by means of the approximated plurality of utilized pressure drop characteristic curves between the respective pressure measuring points at a low flow or a flow of 0 permitting an event-controlled premature break-off of the insufflation phase. Therefore, unlike in the state of the art in which pressure measurement occurs time-controlled, it is not necessary to lower the flow after a fixed time interval in order to be able to measure the intraabdominal pressure.
In this way, a constant or at least an approximately constant gas flow over longer periods of time is provided. Due to the, compared to the state of the art, reduced fluctuations of the gas flow, the condition dependencies change less than in the state of the art. Nonetheless, accurate pressure determination is possible.
In this context, it is advantageous if the control unit generates an alarm if the flow sensor measures a gas flow value of 0, because this value may indicate a defect in the instrument.
Furthermore, an evacuation valve may be located at the proximal part of an instrument inserted in the corporeal cavity is provided in an as such known manner for limiting the intraabdominal pressure.
Therefore, the control unit closes the evacuation valve at intervals duration of which depends on the intraabdominal pressure. Thus, these intervals of the insufflation do not have to be fixed.
Furthermore, it is preferred that a vacuum pump is provided, also in a known manner, for enhancing evacuation.
The invented design, in which the control unit continuously extrapolates thepressure inside the body, permits controlling the vacuum pump in dependence on the intraabdominal pressure.
Moreover, the aforementioned invented design permits using not only an xe2x80x9con/off valvexe2x80x9d, but also a proportional valve the position of which the control unit regulates in dependence on the pressure inside the body.
Another preferred application of the invented measuring principles given in devices in which a heating device is provided in an as such known manner, whichheats the to-be-insufflated gas to a predetermined temperature. This heating device may, by way of illustration, be provided inside on the tubing between the actual device, i.e. between the control device and the instrument or instruments inserted into the body. With regard to the latter preferred embodiment, which is especially advantageous, reference is made to WO 94/28952.
In the case of a device in which the insufflation gas is heated it is especially advantageous if the control unit sets the gas pressure and the gas flow while taking into account the predetermined gas temperature. This reduces the time span until the desired value is reached; moreover the measured value can be corrected according to the set temperature so that the desired/actual setting is improved.
In addition, the invented measuring principle permits another measurement, notably determination of the characteristic flow value of the tubing, i.e. in particular the insufflation tube and the insufflation channel of the endoscopic instruments.
For this purpose the control unit determines the characteristic flow value of the tubing to the corporeal cavity from the gas pressures measured by the pressure sensor at least two different flow values. With the characteristic flow value, the actual value of the pressure inside the corporeal cavity can also be calculated from the value of the gas pressure measured outside the body.
This method has the advantage that it permits exact determination of the, flow-dependent, characteristic flow value without removing the instrument out of the body and therefore independent calculation of the pressure inside the corporeal cavity and the instrument for additional control of the values determined according to the present invention.
For determination of the characteristic flow value, it is necessary to measure at least two difference flow values; measuring at more than two flow values permits increasing precision by redundancy comparison.
Furthermore, the invented device does not require provision of a second tube for measuring the pressure inside the corporeal cavity.
For insufflating gas into the corporeal cavity, endoscopic instruments, such as a Verres needle, can be provided on which the sensors for gas pressure and gas flow are disposed outside the corporeal cavity.
In any event, the invented device has the advantage that, compared to the known devices described in older patent applications, it offers excellent pressure constancy with greater accuracy of pressure measurement although the gas flow may vary drastically.
The remaining construction of the invented device may correspond to the construction of known devices for insufflating gas into a corporeal cavity with regard to the connection for a gas source, to a measuring device and to the control unit provided, by way of illustration, with a microprocessor. In particular, the pressure regulator and the flow regulator can be combined in one component.